//判断是否存在画布
function isCanvasSupported() {
	var elem = document.createElement('canvas');
	return !!(elem.getContext && elem.getContext('2d'));
}

//压缩方法
function compress(event, callback) {
	if(typeof(FileReader) === 'undefined') {
		mui.toast("当前浏览器内核不支持base64图片压缩");
		//调用上传方式  不压缩
	} else {
		try {
			var file = event.currentTarget.files[0];
			if(!/image\/\w+/.test(file.type)) {
				mui.toast("请确保文件为图像类型");
				return false;
			}
			var reader = new FileReader();
			reader.onload = function(e) {
				var image = $('<img/>');
				image.load(function() {
//					console.log("开始压缩");
					var square = 700;
					var canvas = document.createElement('canvas');
					canvas.width = square;
					canvas.height = square;
					var context = canvas.getContext('2d');
					context.clearRect(0, 0, square, square);
					var imageWidth;
					var imageHeight;
					var offsetX = 0;
					var offsetY = 0;
					if(this.width > this.height) {
						imageWidth = Math.round(square * this.width / this.height);
						imageHeight = square;
						offsetX = -Math.round((imageWidth - square) / 2);
					} else {
						imageHeight = Math.round(square * this.height / this.width);
						imageWidth = square;
						offsetY = -Math.round((imageHeight - square) / 2);
					}
					context.drawImage(this, offsetX, offsetY, imageWidth, imageHeight);
					var data = canvas.toDataURL('image/jpeg/png');
					//压缩完成执行回调
					callback(data);
				});
				image.attr('src', e.target.result);
			};
			reader.readAsDataURL(file);
		} catch(e) {
			console.log("压缩失败!");
			//调用上传方式  不压缩
		}
	}
}